Field of the Invention
This disclosure relates to a method of cleaning a liquid discharge head.
Description of the Related Art
Examples of known liquid discharge heads to be used in an inkjet printer or the like include a liquid discharge head of a type which discharges liquid by using a heat-generating resistor. The liquid discharge head of this type includes a channel forming member that forms a flow channel of liquid such as ink and a heat-generating resistor. The heat-generating resistor is formed of an electric thermal conversion element or the like, and is configured to heat liquid rapidly at a contact portion (heat application portion) with liquid located above the heat-generating resistor by generating heat, thereby causing the liquid to foam. By a pressure in association with this foaming, the liquid is discharged from a discharge port, whereby recording on a surface of a recording medium such as paper is achieved. A configuration of the heat-generating resistor covered with an insulation layer for insulating the heat-generating resistor from liquid is known. The heat-generating resistor multiply receives a physical action such as an impact caused by cavitation in association with foaming and contraction of liquid and a chemical action of liquid. Therefore, a configuration in which the heat-generating resistor is covered with a protective layer to protect the heat-generating resistor is known.
In the liquid discharge head, an additive such as color materials contained in liquid is decomposed by being heated at a high temperature, and is changed to a substance with low solubility, so that a phenomenon of being physically adsorbed onto a layer such as the insulation layer or the protective layer which is in contact with liquid may occur. This phenomenon is called a “kogation”. If kogation is adhered onto the protective layer, thermal transfer from a heat application portion to liquid becomes uneven and, consequently, foaming becomes unstable, whereby a liquid discharging property may be affected.
In order to solve the above-described problem, Japanese Patent Laid-Open No. 2008-105364 describes a configuration in which the upper protective layer is arranged in an area including the heat application portion so that it can be electrically connected to serve as an electrode which causes an electrochemical reaction with the liquid and, in addition, a counter electrode is arranged in the same liquid chamber. According to the configuration described in Japanese Patent Laid-Open No. 2008-105364, the upper protective layer serves as an anode electrode and the counter electrode serves as a cathode electrode, so that the upper protective layer is dissolved by the electrochemical reaction, whereby kogation on the heat application portion can be removed.